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PRIVILEGED&CONFIDENTIAL V 6.3 Monitoring Well Abandonment Activities On August 2 and 3, 1999, Building Analytics destroyed four on-site groundwater monitoring wells, two by the over drill method and two by the pressure grout method. All equipment for the destruction of these groundwater monitoring wells were supplied by Gregg Drilling of Martinez, California. The two well destruction methods are %W described below in Sections 6.3.1 and 6.3.2. 6.3.1 Over Drill Method Because TPH and BTEX were reported in Monitoring Well Nos. MW-2 and MW-4, Building Analytics proposed to destroy these two wells by over drilling the wells. The taw wells had a total depth of approximately 70 feet bgs. On AWust 2, 1999, the two wells were over drilled using a Mobile B-61 drill-rig equipped with 12-inch o.d. hollow-stem augers. The well casing, screen, grout and sand pack material were over drilled, by using an auger with a larger diameter than the auger that was originally used (10-inch O.D.) to install the wells. The cuttings (i.e., grout and sand pack material) were placed in 55-gallon Department of Transportation (DOT) approved open-top drums. Subsequent to the removal of the casing, screen and sand pack, the borings were filled with Portland cement grout. A tremy hose was placed near the bottom of the borings, and grout was pumped into the borings from the bottom upwards. The hose was removed slowly as the borings filled with grout. Once the borings were filled with grout, the grout was allowed to settle. Once the grout had settled, the grout in the borings was topped-off to within approximately two feet of the ground surface. Approximately 310 gallons of grout were pumped into each of the drilled out monitoring wells. The well boxes and concrete pads were then removed using a jack-hammer. A concrete cap of approximately two feet thick was then placed on top of the grout in each boring, and the surface refinished to match the existing ground surface. 6.3.2 Pressure Grouting Method `r Because TPH and BTEX were not reported in Monitoring Well Nos. MW-1 and MW-3, Building Analytics proposed to destroy these two wells by the pressure grouting method. The wells had a depth of approximately 70 feet bgs. Wo On August 3, 1999, the two wells were pressure grouted using a trailer mounted grout pump. Prior to grouting each well, a mechanical or pneumatic packer was placed at the ftw top of the well casing. Portland cement grout was then pumped into the wells under pressure through the packer. The borings were filled with grout and then held under approximately 30 to 40 pounds of pressure for approximately five minutes. The packer was then removed and the grout allowed to settle. Once the grout had settled, the upper five feet of well casing was drilled out using a Mobile B-61 drill rig equipped with 12- inch o.d. hollow-stem augers. The cuttings (i.e., grout and sand pack material) were placed in 55-gallon DOT approved open-top drums. The grout in the borings was then topped-off to within approximately two feet of the ground surface. Approximately 80 gallons of grout was pumped into each of the monitoring wells. The well boxes and concrete pads were then removed using a jack-hammer. A concrete cap of approximately two feet thick was placed on top of the grout, and the surface refinished to match the existing ground surface. 6 199164-WFB.Stockton Well Abandonment Rpt. L.r